Crossbar switches

ABSTRACT

The select fingers in a crossbar switch has a movable lever arm which enables at least a reduction in the different operating forces which occur when a select finger is actuated in a free condition as compared to when a select finger is operated in a trapped condition -that is when held by an operating card.

United States Patent [191 Elliott Jan. 23, 1973 CROSSBAR SWITCHES [56] References Cited [75] Inventor: Gilbert Leslie Elliott, Georgetown, m M n- STATES PATENTS Ontario, Canada 6 3,364,447 1/1968 Peek, Jr ..335/l i5 [73] Assignee: Northern Electric Company Limited, 3,509,301 4/1970 DeSmet....

Montreal Quebec, Canada 3,673,366 6/1972 Symes ..200 175 [.22] Filed: March 1972 Primary Examiner Harold Broome 21 Appl' No: 233 7 Att0meySidney T. Jelly [57] ABSTRACT ;J.S.CCll ..335/l12, 200/175 The Select fingers in a crossbar switch has a movable Ill. ..H0lll lever arm enables at least a reduction in the [58] Flew of Search "335/112, 11 1101 115; ferent operating forces which occur when a select 200/175, 177 finger is actuated in a free condition as compared to when a select finger is operated in a trapped condition that is when held by an operating card.

3 Claims, 6 Drawing Figures PATENTEDJAH23I975 3,713 05 SHEET 1 [IF 3 PATENTEDJANZS I975 3.713.054

sum 2 0F 3 VIL I i CROSSBAR SWITCHES This invention relates to crossbar switches, such as are used in telephone systems, and in particular to the selection mechanism for such switches.

Crossbar switches, as used in telephone communication switching offices, are mounted on frames to form a switching complex. In a frame the switches are arranged in rows extending in two directions, for example horizontally and vertically. In operation crosspoint connections are set up by select fingers arranged parallel to one set of rows, for example vertically. The fingers are moved by actuators arranged parallel to the other set of rows, i.e., horizontally. The actuators are mounted on select bar, a select bar for each horizontal row, pivotally mounted at its ends and actuated by a relay.

In sequence a select bar is rotated causing all the select actuators carried by that bar to move in a vertical plane. Each actuator moves a select finger. An armature is positioned alongside each vertical row of select fingers and movement of an armature pushes all the select fingers in the related vertical row in a horizontal direction. At each select finger position is an operating card. At the position in the vertical row corresponding to the horizontal row of the operated select bar, the select finger has been movedto a position whereby actuation of the armature results in that select finger moving the related operating card and closing switch contacts.

It is a feature of crossbar switches that the select fin.- gers are resilient and as long as overall dimensions of the frame permit. This is to reduce operating forces on the select actuators and select bars. However there are two operating conditions for the select fingers. The select fingers move in slot formation in the operating cards. The first time a finger in a vertical row is moved by an actuator, the finger moves in a part of the slot formation which permits deflection of the finger for its full length. However on actuation of the armature all the select fingers in that row are moved horizontally. Those fingers not moved by an actuator move into a second part of the slot formation of the operating cards. It then occurs that a further select bar is actuated. This in turn attempts to move another select finger in the vertical row in which a select finger has been moved. In this instance however deflection of the select finger is restricted to that portion extending between the operating card and the select actuator. The operating forces are much higher in this condition.

It is a feature of these switches that the select fingers are resilient and are made as long as overall dimensions of the frame permit to reduce the operating forces on the select actuators. Actuation of the select actuators moves the select fingers up and down a slot formation in the operating cards. When the fingers have been moved by an actuator it is in a restricted slotportion and operation of the armature causes the finger to move the card.

The present invention is concerned with a select actuator which provides a variable lever arm for the select finger, permitting the select finger travel as previously in the operating mode, that is when the finger is moved to operate the operating card, but reduces the operating force on the select actuator when a finger is actuated when held in an operating card which is in unoperative position, or alternatively providing comparable advantages such as increased finger travel in operational modes without increasing operating forces or intermediate combinations of such advantages.

The invention will be readily understood by the following descriptions of a present used arrangement and our embodiment of the present invention, by way of example, in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a switch frame with one select bar in position and one row of contacts with associated select fingers and operating cards;

FIG. 2 illustrates the row of contacts, with select fingers and operating cards, of FIG. 1, in more detail, in a normal or inoperative condition;

FIG. 3 is similar to FIG. 2 but with the select bar in operated position;

FIG. 4 diagrammatically illustrates a select finger, select actuator and part of an operating card as presently used, to an enlarged scale;

FIG. 5 diagrammatically illustrates a select finger, part of an operating card and one form of select actuator in accordance with the present invention; and

FIG. 6 is a plan view of a select actuator as in FIG. 5.

Illustrated in FIG. 1 is a frame 10 adapted to carry a plurality of rows of contacts, only one row being shown in FIG. 1 at 11; Other rows are positioned in the frame as indicated by the slots 12 in the frame. In the arrangement illustrated the rows 11 are extending vertically parallel to each other.

Extending transversely of the frame l0, that is normal to the rows 11, is a plurality of select bars, only one of which is shown at 13 in FIG. 1. Each select bar 13 carries a series of select actuators 14, an actuator positioned relative to each row 11 of contacts. The select bars are pivotally mounted at the ends by means of armatures l5. Armatures 15 are acted upon by pairs of solenoids l6 and 17, the select bar being rotated about its longitudinal axis in one direction by one solenoid, e.g., l6, and in the other direction by the other solenoid 17.- These rotations move the select actuators up and down, as seen in FIG. 3.

The rowsll, in additionto having the carry select fingers, a finger 18 or 19 respectively for each set of contacts, a pair of fingers being positioned to cooperate with each select actuator 14. Movement of a select actuator upward moves the upper select finger l8 and movement of a select actuator downwards moves the lower select finger 19. Thus it will be seen that actuation of a select bar, for example in a direction to move the select actuators l4 upwards, moves all the upper select fingers 18 the upper finger in each row 11, positioned relative to the particular select bar.

Also carried by each row 11 is a series of operating cards arranged in pairs. These are seen more clearly in FIGS. 2 and 3 at 20. FIG. 2 illustrates the condition when the select bar 13 is in the inoperative position. The select actuators 14 are positioned between the related pairs of select fingers l8 and 19, the fingers being in their inoperative positions.

FIG. 3 illustrates the condition when the select bar 13 has been rotated about its longitudinal axis to move the select actuators 14 upwards as seen in FIG. 3. The

contacts, also,

select actuator 14 related to the row 11 shown in FIG. 3 has moved one of the upper select fingers l8 upwards. Each operating card 20 has a slot formation 31 at its end, having a somewhat reversed L shaped formation. The stem 32 of the slot extends vertically while the base 33 extends normal to the stem. It will be seen that the slot formation of one operating card of a pair has the stem 32 extending upwards this being associated with the upper select finger 18- and the slot formation of the other operating card of a pair has the stem extending downward for the lower select finger 19.

The operating cards 20 are mounted in the rows 11 by being supported on fixed contact members 34 carrying fixed contacts. The form of the operating cards is seen more clearly in FIGS. 4 and 5. The operating cards have the operating end in which has the slot formation 31 and a support portion in which are formed notches 35. The notches 35 fit between the contact members 34 and permit lateral sliding of the operating card. Moving contact members 36 also are positioned in the notches and on such sliding the moving contact members 36 are moved, their contact coming into electrical contact with contacts on fixed contact members 34.

The operating cards are moved laterally through the agency of the select fingers 18 or 19. Extending adjacent to each of the rows 11 is an armature 37. Armature 37 is pivotally supported top and bottom in the frame and at its lower end is in operating relationship with a solenoid 38 (FIG. 1). Energization of the solenoid 38 rotates armature 37 about a longitudinal axis passing through the pivot points of the armature. Considering FIG. 3, the select bar 13 has been moved to lift the select actuators 14 which in turn raises the related top selector finger 18. The main portion of the armature 37 is offset from the pivotal axis and rotation of the armature about this axis results in the main, offset portion moving towards the contact members 34 and 36. Movement of the armature deflects sideways the select finger 18 raised by the selector actuator 14. The selector finger 18 in turn is trapped in the stem portion 32 of the slot formation 3l'of the operatingcard at the position of the raised selector actuator. The selector finger pushes the operating card sideways and this moves the moving contact members 34 bringing contact between the fixed and moving contacts.

The operation described so far is the normal one for cross-bar switches, and this operation will be considered in more detail with respect to the interrelationship between the selector actuators 14, selector fingers 18 and 19 and operating cards 20.

FIG. 4 illustrates in more detail, and to an enlarged scale, the relationship between selector actuator 14, a select finger in this example an upper select finger 18- and an operating card 20. Selection of a crosspoint is by rotation of a select bar 13 (as previously described) thereby moving the select finger in the direction of the arrow Y. When the select finger moves a distance greater than Y (FIG. 4) it enters the stern portion 32 of the slot formation 31. This is known as the trapping zone. With the finger in this zone a crosspoint may be closed by moving the armature 37 (FIGS. 1 and 3) which moves the select finger 18 and operating card 20 in the direction of the arrow X. For a given rotational movement of the select actuator 14, maximum travel of the select finger 18 is obtained by keeping the distance between select actuator 14 and operating card 20 distance B in FIG. 4 to a minimum.

The minimum distance for B is controlled at least to some extent by forces acting on the select mechanism under the most adverse conditions. This condition occurs when a finger is deflected by a select actuator after it has been deflected by an armature. Thus, considering FIG. 4, the select finger 18 is made as long as possible for example by attaching the finger at its end remote from that acted upon by the select actuator 14 as far to the rear of the related row 11 as possible. When closing a cross-point the select finger moves into the stem portion 32 of the slot formation 31 of the operating card 20 and the full length of the finger is available for deflection. If however the armature 37 has been actuated to close a cross-point at another position on the same vertical unit, or row 11, the select fingers will have been moved by the armature in a direction normal to that direction in which the select fingers are moved by the select actuators. If then a select bar at a position other than that at which a crosspoint has been made is actuated, the select actuator will deflect its related select finger but instead of being able to deflect up into the stern portion 32 it will be held in the base portion 33. There will only be the length from the operating card 20 to the select actuator 14 available for deflection. This is the length B, FIG. 4, and the condition is illustrated by the dotted lines 40. The normal, free, length of the select finger is the length A, FIG. 4. This reduction in length increases the operating force, and this force limits the select finger travel which can be obtained with a particular arrangement.

The present invention provides an arrangement whereby the effective lever arm for the select finger 18 is varied such that the travel of a finger can be increased without any increase in the operating force when the finger is held in the base portion of an operating card, or the operating force reduced for the same finger travel, or some intermediate combination. FIGS. 5 and 6 illustrate a particular arrangement in which the bent end 41 of the select actuator 14 is at an angle 0 greater than 90, as compared with the conventional configuration, as in FIG. 4, in which the bent end is at 90". By this arrangement, the point of contact between select actuator and finger, indicated at 42 in FIG. 5, is nearer to the operating card 20 than the position 43 which is the contact point between finger and actuator when the finger is in the base 33 of the slot formation 31. Also, for the same length of select actuator from the select bar to the bend 44 in the finger, point 42 is farther from the select bar which is the axis of the rotation for the select actuatorthan the point 43. Both these features provide greater select finger'travel for the select condition when the finger moves in the stem portion 32 of the slot formation 31, other details of the select finger remaining as the conventional configuration, as in FIG. 4, that is when distance B in FIG. 5 is the same as this distance in FIG. 4.

Certain limitations apply in that too great an angle 0 will cause malfunctioning of the select finger actuation. As the select bar 13 (FIGS. 1 to 3) rotates to lift the select actuator, the bent portion 41 will become inclined. In particular as seen in FIG. 5 the bent portion at the maximum rotation of the select actuator 14 will have made an effective rotation of relative to a horizontal plane. The larger the angle 0, the larger the angle d). if angle is too large the select finger, being resilient or springy, will tend to slide down the select actuator as the select actuator moves. The angle (1) is therefore controlled by the value of the coefficient of friction between select actuator 14 and select finger 18. In one particular arrangement it has been found that a correlation between angles 0 and 4: and the coefficient of dynamic friction p. can be as follows:- Tan 0.Sin 11 The value of p. can be modified, such as by covering either the end of the select finger 18 or the bent end 41 of the select actuator 14 or both, with a suitable material such as natural or synthetic rubber or by roughening the surfaces of the finger and/or actuator.

The invention considerably improves the operation of crossbar switches. In the switch frame illustrated in FIG. 1, there are five select bars 13, and twenty rows or units 11. Thus there are one hundred crosspoints. At any one time there is likely to be a large number of select fingers being actuated or moved in a condition when the fingers can deflect only over that part of their length between the operating card 20 and the select actuator 14. Thus, in order to keep the power requirements within reasonable limits there is a compromise between the maximum power applied to the select bars 13 and the maximum deflection of the select fingers 18 and 19. The present invention facilitates this compromise, permitting increased deflection at no increase in maximum power, reduced power for the same deflection or some intermediate arrangement.

What is claimed is:

l. A crossbar switch comprising a resilient select finger; a select actuator adapted to move the select finger in a first direction, and an armature adapted to move the select finger in a second direction normal to said first direction, to a crosspoint selection position; an operating card mounted for movement transverse to the direction of movement of the select finger by the select actuator, the operating card including a slot formation having a stem portion extending in the direction of movement of the select finger in the first direction and a base portion extending normal to the stern portion, the select finger moving into the stem portion when moved initially in said first direction, when the operating card is in the non-operated position and moving into the base portion when moved initially in said second direction when the operating card is in the nonoperated position; the lever arm of the select finger being longer when the select actuator deflects the select finger initially in the second direction than when deflected initially in the first direction.

2. A crossbar switch as claimed in claim 1, the select actuator including a main portion extending parallel to the plane of movement of the select finger and an end portion extending in a direction transverse to the main portion and positioned to engage the select finger, the end portion extended at an indicated angle of 0, 6 being greater than 3. A crossbar switch as claimed in claim 2, the rotation of the end portion of the select actuator corresponding to and the relationship between 0 and qb being Tan 0.S in 2 u, where u is the coefficient of dynamic friction between the select finger and the select actuator. 

1. A crossbar switch comprising a resilient select finger; a select actuator adapted to move the select finger in a first direction, and an armature adapted to move the select finger in a second direction normal to said first direction, to a crosspoint selection position; an operating card mounted for movement transverse to the direction of movement of the select finger by the select actuator, the operating card including a slot formation having a stem portion extending in the direction of movement of the select finger in the first direction and a base portion extending normal to the stem portion, the select finger moving into the stem portion when moved initially in said first direction, when the operating card is in the non-operated position and moving into the base portion when moved initially in said second direction when the operating card is in the nonoperated position; the lever arm of the select finger being longer when the select actuator deflects the select finger initially in the second direction than when deflected initially in the first direction.
 2. A crossbar switch as claimed in claim 1, the select actuator including a main portion extending parallel to the plane of movement of the select finger and an end portion extending in a direction transverse to the main portion and positioned to engage the select finger, the end portion extended at an indicated angle of theta , theta being greater than 90*.
 3. A crossbar switch as claimed in claim 2, the rotation of the end portion of the select actuator corresponding to phi *, and the relationship between theta and phi being Tan theta .Sin > or = Mu , where Mu is the coefficient of dynamic friction between the select finger and the select actuator. 